1. Field of the Invention
The present invention relates generally to bistable multivibrators as used in logic design, and more particularly to a master/slave flip-flop.
2. Description of the Prior Art
The use of multivibrators in logic design is well known to those of reasonable skill in the art, as is the more specific use of a master/slave flip-flop. This form of macro has been used virtually throughout the field of logic systems and has been used successfully as a versatile design tool for many logic purposes.
U.S. Pat. No. 5,164,612, to Kaplinsky which describes a master/slave flip-flop which is altered to selectively become transparent to the data signal. This purpose is accomplished by the addition of a new driver stage within the flip-flop, or by the addition of multiplexers to provide, for example, the necessary "latch" or "unlatch" signals to the master/slave flip-flop.
A plurality of flip-flops (memory cells) that are programmed by a user to create the desired architecture for the device in use is described in U.S. Pat. No. 4,940,909, to Mulder, et al. A plurality of shift registers are connected to the flip-flops for storage of the programming signal so that it is not destroyed during testing of various architectural configurations.
U.S. Pat. No. 4,616,338, to Helen, et al, in which a FIFO type temporary storage system utilizes registers which may comprise a plurality of transparent data type flip-flops for the storage and adds further handling logic for controlling the register flip-flops. Data type flip-flops may be rendered transparent by holding the clock to a high state. However, such flip=flops are not useful for applications which cannot tolerate the relatively lengthly metastable state.
U.S. Pat. No. 5,095,454, to Huang, in which a system for verifying timing during path tracing through digital circuitry uses flip-flops as the path end points, which flip-flops may be of a transparent latch-based design. This design utilizes the clock signal as the transparency input to the flip-flop, and when the block is not present the macro reverts to latching;
A phase-selectable flip-flop has an input transparent latch which makes the output flip-flop switch from transparency to latching depending on the phase of the clock signal in U.S. Pat. No. 5,004,933, to Widener.
U.S. Pat. No. 5,155,382, to Madden, et al, in which a master/slave flip-flop is connected to the clock signal in a manner intended to prevent a race-through condition.
Though data type flip-flops may be rendered transparent using only the clock signal, such devices are not useful for many data latching functions. However, because of the added complexity of master-slave flip-flops, programmable transparency is not easily accomplished for the enhanced testing advantages it offers. As can be seen, the prior art devices tend to add great complexity to the system, thus exacerbating rather than improving reliability and maintainability.